Fluorescein 6-isothiocyanate is widely used as a fluorescent labeling reagent in biochemistry and molecular biology. It is particularly valuable for tagging proteins, antibodies, and other biomolecules due to its strong fluorescence and ability to form stable covalent bonds with primary amines. This property makes it a key tool in fluorescence microscopy, flow cytometry, and immunofluorescence assays, enabling researchers to visualize and track specific molecules within cells or tissues. Additionally, it is employed in diagnostic applications, such as detecting and quantifying biomolecules in clinical samples. Its high sensitivity and compatibility with various detection systems make it a versatile choice for both research and diagnostic purposes.